AbstractDaphnia magnawere exposed to cadmium, copper and cyanazine to determine the relative sensitivities of several age groups: less than 4 h, less than 24 h, 1 d, 2 d, 3 d, 4 d, 5 d and 6 d old. Mean cadmium 48‐h EC50 values for each age group ranged from 23 to 164 μg/L. Mean copper EC50 values ranged from 6 to 18 μg/L. Cyanazine EC50 values ranged from 53 to 106 mg/L. The 1‐d‐old and 5‐d‐oldDaphniamean EC50s were 48 and 49 μg/L for cadmium, 10 and 10 μg/L for copper and 84 and 86 μg/L for cyanazine, respectively. These similar sensitivities indicate that older animals can be used in tests equally as well as younger animals, thus simplifying the recovery of daphnids in acute sediment
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